Prediction of smoking relapse and difficulty during quit attempts will increase in importance as we try to match the characteristics of smokers and treatments, thereby increasing the probability of success. Methods used to assess pharmacological aspects of nicotine dependence have shown some promise as screening instruments, but little is known about nonpharmacological aspects of nicotine dependence, their interrelationships with pharmacological aspects, and the relationship of the various nicotine dependence dimensions to the course and outcome of attempts to quit smoking. Moreover, very little is known about nicotine dependence in smokers who will try to quit on their own or with minimal assistance, who represent the majority of smokers who wish to quit. This study will assess pharmacological and nonpharmacological dimensions of nicotine dependence in a sample of smokers who wish to quit on their own. Measures will include smoking motives, smoking temptations, reactivity to smoking cues, behavioral and biological parameters of nicotine intake, nicotine tolerance, and regulation of blood nicotine levels. Smokers will be assessed before they quit smoking, and they will be followed repeatedly in time for one year after attempted cessation. The measures of nicotine dependence will be used to construct and contrast several multidimensional theories on nicotine dependence. Multidimensional nicotine dependence profiles will be constructed according to the best fitting theoretical model. Smokers will be grouped according to similarity of nicotine dependence profiles, and group differences will be examined on intensity and duration of nicotine withdrawal symptoms, time until relapse and situational antecedents of relapse. The results of this study will advance our understanding of the nature of nicotine dependence and will have direct implications for future studies which utilize assessments to screen and match smokers to appropriate treatments.